The invention relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field has a component parallel to the liquid-crystal layer that is crucial for the realignment, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one mesogenic compound of the formula I.
In conventional liquid-crystal displays (TN, STN, OMI or AMD-TN), the electric fields for realignment are generated essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are generated in such a way that the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operating a display of this type are described, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).
EP 0 588 568, for example, discloses various possibilities for the design of the electrodes and for addressing a display of this type. DE 198 24 137 likewise describes various embodiments of IPS displays of this type.
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104.
The IPS displays containing the known liquid-crystalline media are characterised by inadequate, long response times and often excessively high operating voltages. There is thus a demand for IPS displays which do not have these disadvantages or only do so to a reduced extent. To this end, in particular liquid-crystalline materials are required which, besides an adequate phase range, low tendency towards crystallisation at low temperatures, low birefringence and adequate electrical resistance, have, in particular, low threshold voltages (V10) and low rotational viscosities (xcex31), which are crucial for the response times.
This object has, surprisingly, been achieved by the use of liquid-crystalline materials in mixtures which comprise at least one compound of the formula I.
The IPS mixtures according to the invention are distinguished by their relatively low rotational viscosity values xcex31 and their low threshold voltage and response time values.
The invention thus relates to an electro-optical liquid-crystal having a realignment layer for realignment of the liquid crystals whose field has a significant component parallel to the liquid-crystal layer, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one compound of the formula I 
in which
R1 is an alkyl or alkenyl radical having up to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen and in which, in addition, one or more CH2 groups in these radicals may each, independently of one an other, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, 
xe2x80x83xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 or xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 in such a way that O atoms are not linked directly to one another, and
L is H or F.
Particular preference is given to compounds of the formula I in which L is F.
In the compounds of the formula I, R1 is preferably alkyl or alkenyl having up to 7 carbon atoms. R1 is preferably ethyl, n-propyl, n-pentyl, vinyl, 1E-alkenyl or 3E-alkenyl.
The compounds of the formula I have high dielectric anisotropy values and relatively high birefringence and clearing point values. Their use in liquid-crystal mixtures for IPS displays according to the invention facilitates high dielectric anisotropies and low rotational viscosities with retention of high clearing points and favourable birefringence values and effects low threshold voltages and short response times.
It has been found, in particular, that IPS mixtures according to the invention comprising one or more, preferably one or two, compounds of the formula I have significantly higher dielectric anisotropy values, lower rotational viscosity and threshold voltage values, as well as shorter response times than, for example, analogous mixtures which, instead of the compounds of the formula I, comprise 3,5-difluoro-4-cyanophenylcyclohexanes of the formula 
Some of the compounds of the formula I are disclosed in DE 40 27 869 A1. However, this patent application does not describe IPS displays.
Preferred embodiments are IPS displays in which
a) the liquid-crystalline medium additionally comprises one or more compounds of the formula II containing a cyano group 
xe2x80x83in which
R2 is H, an alkyl or alkenyl radical having up to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least mono-substituted by halogen and in which,,in addition, one or more CH2 groups in these radicals may also each, independently of one another, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, 
xe2x80x83xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 or xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 in such a way that O atoms are not linked directly to one another,
A1 and A2 are each, independently of one another,
(a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene radical, in which, in addition, one more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
(b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
(c) a radical from the group consisting of 1,4 bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a), (b) and (c) may be substituted by one or two fluorine atoms,
Z1 and Z2 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHFxe2x80x94CHFxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CF2CF2xe2x80x94 or a single bond, and one or the radicals Z1 and Z2 is alternatively xe2x80x94(CH2)4xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CH2CH2xe2x80x94,
L1 and L2 are each, independently of one another, H or F, and
m is 0, 1 or 2,
b) the liquid-crystalline medium comprises one or more compounds of the formula III containing a 3,4,5-trifluorophenyl group 
xe2x80x83in which
R3 has one of the meanings indicated for R2 in the formula II,
A3 and A4 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
Z3 and Z4 each, independently of one another, have one of the meanings indicated for Z1 and Z2 in the formula II, and
n is 0, 1or 2,
c) the liquid-crystalline medium comprises one or more compounds of the formula IV
R4-(A5-Z5)o-A8-R5xe2x80x83xe2x80x83IV
in which
R4 and R5 each, independently of one another, have one of the meanings indicated for R2 in the formula II,
A5 and A6 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
each Z5, independently of the others, has one of the meanings indicated for Z1 and Z2 in the formula II, and
o is 1, 2 or 3
d) the liquid-crystalline medium additionally comprises one or more compounds of the formula V 
xe2x80x83in which
R6 has one of the meanings indicated for R2 in the formula II,
A7 and A8 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
Z7 and Z8 each, independently of one another, have one of the meanings: indicated for Z1 and Z2 in the formula II,
L1 and L2 are each, independently of one another, H or F,
Q is a polyfluoroalkylene radical of the formula:
xe2x80x94(O)qxe2x80x94(CH2)rxe2x80x94(CF2)sxe2x80x94,xe2x80x94(O)qxe2x80x94(CHF)rxe2x80x94(CF2)sxe2x80x94 or
xe2x80x94(O)qxe2x80x94(CF2)rxe2x80x94(CHF)sxe2x80x94CF2xe2x80x94, in which
q is 0 or 1,
r is 0, 1, 2, 3, 4, 5 or 6,
s is 1, 2, 3, 4, 5 or 6,
X is H, F or Cl, and
p is 0, 1 or 2, and/or
e) the liquid-crystalline medium additionally comprises one or more compounds of the formula IIIxe2x80x2
xe2x80x83in which
R3xe2x80x2 has one of the meanings indicated for R2 in the formula II,
A3xe2x80x2 and A4xe2x80x2 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
Z3xe2x80x2 and Z4xe2x80x2 each, independently of one another, have one of the meanings indicated for Z1 and Z2in the formula II, and
nxe2x80x2 is 0, or 2.
The compounds of the formula II are preferably selected from the group comprising the formulae IIa to IIq: 
in which R2 is as defined in the formula II, and L1 and/or L2 is H or F.
In the compounds of the formulae IIb, IIe, IIk, IIn and IIp, L2 is particularly preferably F. In the compounds of the formulae IId, IIg, IIh and IIi, L2 is particularly preferably H. In the compounds of the formula IIo and/or IIp, L1 and L2 are preferably fluorine.
The liquid-crystalline medium particularly preferably comprises one or more compounds selected from the group consisting of the compounds of the formulae IIa, IIb, IIc, IId, IIh, IIk and IIp.
In a further preferred embodiment, the liquid-crystalline medium comprises at least one heterocyclic compound selected from the group comprising the formulae IIm, IIn, IIo and IIp.
The compounds of the formula III are preferably selected from the group comprising the formulae IIa to IIIp and IIIxe2x80x3a, 
in which R3 is as defined in the formula III.
The liquid-crystal display particularly preferably contains a liquid-crystalline medium comprising one or more compounds selected from the group comprising the formulae IIIc, IIId, IIIe, IIIf, IIIg, IIIh, IIIi, IIIk and IIIn.
The compounds of the formula IIIxe2x80x2 are preferably selected from the group comprising the formulae IIIxe2x80x2a to IIIxe2x80x2l: 
in which
R3xe2x80x2 is as defined above under the formula IIIxe2x80x2.
As an alternative to or in addition to one or more compound(s) of the formula IIIc, the liquid-crystalline medium may comprise one or more compounds of the formula IIIxe2x80x2a, 
in which R3xe2x80x2 is as defined above under the formula IIIxe2x80x2.
The compounds of the formula IV are preferably selected from the group comprising the formulae IVa to IVn: 
in which R4 and R5 are as defined in the formula IV, and L is H or F.
In the compounds of the formula IVj, L is particularly preferably F.
The liquid-crystal display particularly preferably contains a liquid-crystalline medium comprising one or more compounds selected from the group consisting of the compounds of the formulae IVb, IVe, IVk and IVm.
The compounds of the formula V are preferably selected from the group comprising the formulae Va to Vm: 
in which R6 is as defined in the formula V, and L2 is H or F.
In the compounds of the formula Vd, L2 is particularly preferably F.
The liquid-crystalline medium particularly preferably comprises one or more compounds selected from the group consisting of the compounds of the formulae Va, Vc, Vd, Ve and Vf.
In a preferred embodiment, the liquid-crystalline medium comprises one or two compounds of the formula I and one or two compounds of the formula Ve.
In a further preferred embodiment, the liquid-crystalline medium comprises one or more alkenyl compounds of the formula VI 
in which
R7 is an alkenyl group having 2 to 7 carbon atoms,
Z9 is xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CH2CH2- or a single bond,
L is H or,F,
a is 0 or 1 and
R8 is an alkyl, alkoxy or alkenyl group having up to 12 carbon atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by xe2x80x94COxe2x80x94, xe2x80x94OCOxe2x80x94 or xe2x80x94COOxe2x80x94, or, if a is 1, R8 may alternatively be F.
The compounds of the formula VI are preferably selected from the group comprising the formulae VIa to VIf: 
in which
k is 1, 2, 3, 4 or 5,
y and z are each, independently of one another, 0, 1, 2 or 3, where y+z is  less than xe2x89xa65, and
x is 0 or 1.
In the compounds of the formula VIf, L is preferably F.
The mixtures according to the invention preferably comprise one or two compounds of the formula IVb and one or two compounds of the formula VIa.
Further preferred embodiments are the following mixtures for IPS displays:
The medium additionally comprises one or more compounds containing a 4-fluoro-phenyl group, selected from the group consisting of the formulae VIIa to VIIc: 
xe2x80x83in which R9 has the one of the meanings indicated for R3 in the formula III, and in particular is alkyl having 1 to 7 carbon atoms;
The medium additionally comprises one or more compounds of the formula VIII 
xe2x80x83in which R10 and R11 are each, independently of one another, straight-chain alkyl or alkoxy; preferably alkyl, having 1 to 7 carbon atoms;
The medium additionally comprises one or more compounds of the formula IX 
xe2x80x83in which R12 has one of the meanings indicated for R1.
The medium additionally comprises one or more compounds of negative dielectric anisotropy selected from the group consisting of the formulae X, XI and XII: 
xe2x80x83in which R13 and R14 each, independently of one another, have one of the meanings indicated for R1, and b is 0 or 1. R13 and R14 are preferably straight-chain alkyl or alkoxy having 1 to 7 carbon atoms, furthermore alkenyl or alkenyloxy having up to 7 carbon atoms. In particular, R13 is preferably alkyl and R14 is preferably alkoxy.
The medium additionally comprises one or more difluorostilbenes of the formula XIII, 
xe2x80x83in which
Alkyl* and Alkyl** are a straight-chain alkyl radical having 1 to 6 carbon atoms, preferably 2 to 5 carbon atoms.
The % proportion of the difluorostilbenes in the mixture according to the invention is from 0 to 30% by weight, preferably from 0 to 20% by weight, in particular from 0 to 15% by weight.
The medium additionally comprises one or more compounds of the formula XIV 
in which
R15 is as defined for R1 , and
L1 and L2 are each, independently of one another, H or F.
The proportion of the compounds of the formula XIV in the mixture according to the invention is from 0 to 30% by weight, preferably from 0 to 20% by weight, in particular from 0 to 15% by weight.
The medium additionally comprises one or more compounds of the formula XV 
in which
R16 is as defined for R1, preferably is straight-chain alkyl or alkoxy having 1 to 3 carbon atoms.
The % proportion of the biphenyls in the mixture according to the invention is from 0 to 30% by weight, preferably from 0 to 20% by weight, in particular from 0 to 15% by weight.
Preference is given to displays containing liquid-crystal mixtures comprising
one or more cyano compounds selected from the group comprising the formulae IIa, IIb, IId, IIg and IIk, in particular compounds of the formulae IIb, IIg and IIk in which L2 is F, and compounds of the formula III in which L2 is H,
one or more dioxane compounds selected from the group comprising the formulae IIk and III, in particular of the formula III in which L2 s F,
one or more 3,4,5-trifluorophenyl compounds selected from the group comprising the formulae IIIc, IIIf, IIIg and IIIh,
one or more compounds selected from the group comprising the formulae IVb, IVh, IVk and IVm. R4 and R5 are preferably straight-chain alkyl having 1 to 7 carbon atoms.
In the compounds of the formula IVb, R5 is preferably alkoxy having 1 to 5 carbon atoms. In the compounds of the formula IVj, L is preferably F,
one or more compounds selected from the group comprising the formulae Va, Vb, Vd and Ve,
one or more alkenyl compounds selected from the group comprising the formulae VIa, VIb, VIe and VIf,
in the compounds of the formula VIa, y and z are particularly preferably 0 or 1,
in the compounds of the formula VIb, z is preferably 0,
in the compounds of the formula VIe, k is preferably 0,
in the compounds of the formula VIf, L is preferably F, and y and z are preferably 0.
Preference is furthermore given to a liquid-crystal display according to the invention in which the pixels are addressed by means of an active matrix.
The invention furthermore relates to a liquid-crystalline medium of positive dielectric an isotropy comprising at least one compound of the formula 1, at least one compound selected from the group consisting of the compounds of the formulae IIa to IIp, IIIa to IIIo and Va to Vk, at least one compound selected from the group consisting of the compounds of the formulae VIa to VIf, and, if desired, one or more compounds selected from the group consisting of the compounds of the formulae IVa to Ivn.
Particular preference is given to mixtures which comprise
The liquid-crystalline media used in accordance with the invention generally have a birefringence (xcex94n) of  less than 0.14, preferably in the range from 0.06 to 0.13, in particular in the range from 0.09 to 0.12; with clearing points of from 60 to 95xc2x0 C., in particular from 65 to 85xc2x0 C.
The flow viscosity xcexd20 (at 20xc2x0 C.) of the mixtures used in accordance with the invention is generally less than 30 mm2xc2x7sxe2x88x921, in particular between 15 and 25 mm2xc2x7sxe2x88x921. The specific resistance of the materials according to the invention is generally, at 20xc2x0 C., from 5xc3x971010 to 5xc3x971014 xcexa9xc2x7cm, the values are particularly preferably from 5xc3x971011 to 5xc3x971013 xcexa9xc2x7cm. The rotational viscosity xcex31 of the mixtures according to the invention is, at 20xc2x0 C., preferably less than 80 mPaxc2x7s, in particular less than 65 mPaxc2x7s.
The clearing point of the media used in accordance with the invention is greater than 60xc2x0 C., preferably greater than 65xc2x0 C. and particularly preferably 70xc2x0 C. or greater. In particular, the clearing point is in the range from 60xc2x0 C. to 85xc2x0 C.
The shelf life in test cells, determined as described below, is 1000 hours or more at xe2x88x9230xc2x0 C., preferably 500 hours or more at xe2x88x9240xc2x0 C. and very particularly preferably 1000 hours or more at xe2x88x9240xc2x0 C.
The media used in accordance with the invention consist of from 5 to 30 compounds, preferably of from 6 to 20 compounds and particularly preferably of from 7 to 16 compounds. The mixtures according to the invention preferably comprise one or two compounds of the formula I.
It has been found that even a relatively low proportion of compounds of the formula I in a mixture with conventional liquid-crystal materials, but in particular with one or more compounds selected from the group consisting of the compounds of the formulae IIa to IIp and/or from the group consisting of the compounds of the formulae IVa to IVn, results in a significant lowering of the threshold voltage, in very low rotational viscosity values xcex31 and in fast response times, with, in particular, broad nematic phases with low smectic-nematic transition temperatures being observed. The compounds of the formulae I to VI are colourless, stable and readily miscible with one another and with other liquid-crystal materials.
The term xe2x80x9calkylxe2x80x9d covers straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atoms are preferred.
The term xe2x80x9calkenylxe2x80x9d covers straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E-alkenyl, C5-C7-4-alkenyl, and C6-C7-5-alkenyl and C7-6-alkenyl, in particular C2-C7-1 E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4-alkenyl. Examples of very particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3E-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are preferred.
The term xe2x80x9cfluoroalkylxe2x80x9d preferably covers straight-chain groups having a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.
The term xe2x80x9calkoxyalkylxe2x80x9d preferably covers straight-chain radical s of the formula CnH2n+1xe2x80x94Oxe2x80x94(CH2)m, in which n and m are each, independently of one another, from 1 to 6. Preferably, m=1 and n is from 1 to 4.
Through a suitable choice of the meanings of R1 to R14, the addressing times, the threshold voltage, the steepness of the transmission characteristic lines, etc., can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals 2E-alkenyloxy radicals and the like generally result in shorter addressing times, improved nematic tendencies and a higher ratio of the elastic constants k33 (bend) and k11 (splay) compared with alkyl and alkoxy radicals. 4-alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k33/k11 compared with alkyl and alkoxy radicals.
The optimum mixing ratio of the compounds of the formulae I-VI depends substantially on the desired properties, on the choice of the components of the formulae I, II, III, IV, V and/or VI and on the choice of any further components present. Suitable mixing ratios within the range indicated above can easily be determined from case to case.
The total amount of compounds of the formulae I to VI in the mixtures according to the invention is not crucial. The mixtures preferably chain of 50-90% a weight of compounds of the formulae I to VI. The mixtures may also comprise one or more further components in order to optimise various properties. However, the observed effect, particularly on the low-temperature stability, is generally greater the higher the total concentration of compounds of the formulae I to VI.
The liquid-crystalline media according to the invention preferably comprise from 2 to 40, in particular from 4 to 30, compounds as further constituents besides one or more compounds of the formula I. These media very particularly preferably comprise from 7 to 25 compounds besides one or more compounds of the formula I. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexane-carboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of, cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexyl-cyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4xe2x80x2-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most important compounds suitable as further constituents of media according to the invention can be characterised by the formulae 1, 2, 3, 4 and 5:
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are each, independently of one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1 ,4-cyclohexylene or 1,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl, and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr, E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are referred to by the sub-formulae 1 a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, which is known as group B, Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3xe2x88x92(k+l)FkClI, where i is 0 or 1, and k+l is 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are referred to by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1 b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, SF5, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is xe2x80x94CN; this sub-group is referred to below as group C, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1 c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1 a-5a and is preferably alkyl, alkoxy or alkenyl.
Besides the preferred compounds of groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents are also customary. All these substances are obtainable by methods which are known from the literature or analogously thereto.
Besides the compounds of the formula I to VI, the media according to the invention preferably comprise one or more compounds selected from group A and/or group B and/or group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably
the sum of the proportions by weight of the group A and/or B and/or C compounds present in the respective media according to the invention preferably being from 5% to 90% and in particular from 10% to 90%.
The structure of the IPS display according to the invention corresponds to the usual design for displays of this type, as described, for example, in WO 91/10936 or EP 0 588 568. The term usual design is broadly drawn here and also covers all derivatives and modifications of the IPS display, in particular, for example, also matrix display elements based on poly-Si TFT or MIM.
However, an essential difference of the displays according to the invention from those usual hitherto consists in the choice of the liquid-crystal parameters of the liquid-crystal layer.
The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner conventional per se. In general, the desired amount of the components used in smaller amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to prepare the mixtures in other conventional manners, for example by use of pre-mixtures, for example homologue mixtures, or using so-called xe2x80x9cmultibottlexe2x80x9d systems .
The dielectrics may also comprise further additives known to the person skilled in the art for described in the literature. For example, 0-15% preferably 0-10%, of pleochroic dyes and/or chiral dopants may be added. The individual compounds added are employed in concentrations of from 0.01 to 6% and preferably from 0.1 to 3%. However, the concentrations given here for the other constituents of the liquid-crystal mixtures, i.e. the liquid-crystalline or mesogenic compounds, are indicated without taking into account the concentration of these additives.
The physical properties of the liquid-crystal mixtures are determined in accordance with xe2x80x9cPhysical Properties of Liquid Crystalsxe2x80x9d Ed. W. Becker, Merck KGaA, as of Nov. 1997, unless explicitly stated otherwise.
C denotes a crystalline phase, S a smectic phase, SC a smectic C phase, SA a smectic A phase, N a nematic phase and I the isotropic phase.
V0 denotes the capacitive threshold voltage. xcex94n denotes the optical anisotropy, and n0 the ordinary refractive index (in each case at 589 nm). xcex94∈ denotes the dielectric anisotropy (xcex94∈=∈∥xe2x88x92∈xe2x8axa5, where ∈∥ denotes the dielectric constant parallel to the longitudinal molecular axes and ∈xe2x8axa5 denotes the dielectric constant perpendicular thereto, in each case at 1 kHz). The electro-optical data were measured in a planar cell at 20xc2x0 C., unless expressly stated otherwise. All physical properties are indicated and measured at 20xc2x0 C., unless expressly stated otherwise.
The cells are preferably bright in the xe2x80x9coffxe2x80x9d state.
The examples below are intended to illustrate the invention without representing a limitation. Above and below, percentages are per cent by weight. All temperatures are indicated in degrees Celsius. xcex94n denotes optical anisotropy (589 nm, 20xc2x0 C), xcex94∈ denotes the dielectric anisotropy (1 kHz, 20xc2x0 C.), H.R. denotes the voltage holding ratio (at 100xc2x0 C., after 5 minutes in an oven at 1 V). The capacitive threshold voltage V0 was determined at 20xc2x0 C. and 1 kHz.
The calibrated rotational viscometer gave a rotational viscosity xcex31 for ZLI-4792 (Merck KGaA) of 133 mPaxc2x7s at 20xc2x0 C.
The shelf life was investigated in sealed test cells with an optical retardation of about 0.5 xcexcm with CU-1511 from DuPont, USA, as alignment layer. To this end, in each case five test cells were bonded on both sides to crossed polarisers and stored at fixed temperatures of 0xc2x0 C., xe2x88x9210xc2x0 C., xe2x88x9220xc2x0 C., xe2x88x9230xc2x0 C. and xe2x88x9240xc2x0 C. At intervals of 24 hours in each case, the cells were assessed visually for changes. The storage time noted at the respective temperature tstore (T) was the final time at which a change was just not observed in any cell.
In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by means of acronyms, the transformation into chemical formulae taking place in accordance with Tables A and B below. All radicals CnH2n+1 and CmH2m+1 are straight-chain alkyl radicals having n, respectively m, carbon atoms. The coding in Table B is self-evident. In Table A, only the acronym for the parent structure is indicated, followed in individual cases, separated from the acronym for the parent structure by a dash, by a code for the substituents R1, R2, L1 and L2:
Preferred displays contain media comprising one or more compounds from Tables A and B in addition to one or more compounds of the formula I.